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State of the UNION This is an off-site link.  Please review our Terms of Service for additional information.


(Norvald H. Ryeng) Since union queries were introduced in MySQL 4.0.0, they have been processed by executing each part of the union and adding the result to a temporary table. Then a final query block is executed that, if needed, filters out duplicates, do global ordering and limit the number of output rows.

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